The zig-zag is the earliest symbolic motif recorded: Neanderthals used this sign around 40,000 B.C. or earlier. From Upper Paleolithic engravings to the vase painting for the first phases of the Cucuteni culture, the "M" or extended "M" sign appear within uterine or vulvar shapes. The zig-zag alternates with the "M" sign, an abbreviated zig-zag. There is a suggested symbolic affinity between these motifs, female moisture and amniotic fluid. Water bieng a symbol for a generative force.
The Language of the Goddess, Marija Gimbutas Pg. 19-20